I am in a 3 year old house and all plumbing worked fine when I took possession. Recently (last 4 months or so) the master bath tub makes a gulping noise as if it's not properly vented when draining. We also notice that when the master bath shower is used (separate from tub) there is a banging noise coming from the drain. All the other baths and drains work fine. Is it possible to get a air lock in the drains? Anyone have any ideas of the cause and possible remedies? Thanks